3.5 Bi-directional power flow

In this scenario, a distributed generation and an energy storage are connected to the DC link of the SST, with a voltage operation of 1144 V as presented in Figure 15. Solid-State Transformer for Energy Efficiency Enhancement DOI: http://dx.doi.org/10.5772/intechopen.84345

Figure 15.

Electrical diagram for a bi-directional power flow.

#### Figure 16.

presents an increment in the magnitude voltage and a decrement in the current load; consequently the active and reactive power behavior is as given in Figure 13. The power factor in the load side does not affect the power factor at the input side (grid), as shown in Figure 14. It is verified that the SST can operate normally with

Overload waveform behavior: (a) grid voltage, (b) load voltage, (c) grid current, and (d) load current.

In this scenario, a distributed generation and an energy storage are connected to the DC link of the SST, with a voltage operation of 1144 V as presented in Figure 15.

an overload of 125%, and the power factor improves.

Power factor behavior at the (a) grid side and (b) load side.

Overload power behavior at the (a) grid side and (b) load side.

Research Trends and Challenges in Smart Grids

3.5 Bi-directional power flow

Figure 12.

Figure 13.

Figure 14.

132

(a) Generator active and reactive power, (b) generator power factor, (c) R-L load power factor, (d) power factor of the distributed energy source, and (e) power of the distributed energy source and the storage energy.

Initially, a load of 50% of their nominal demand is connected; later the load increases to 100% with a power factor of 0.85 lagging, as shown in Figure 16(c).

It is observed that at t ¼ 0:07 s, the distributed generation starts to deliver active power, as shown in Figure 16(d). Then the input power coming from the grid decreases until reaching a negative value as presented in Figure 16(a); this means that the distributed generation is delivering power to the load and the grid. Then at t ¼ 0:17 s, the load increases its demand; that means, there is more power consumption by the load, and this causes the grid to start delivering power to the load. The simulation continues in such a way that the distributed generation is switched off and instead the storage energy starts operating.

network. Several types of topologies can be considered depending on the application. For instance, in a star-type topology, the communication linkage is established between each SSTs and the control center directly. Other topologies allow improved connectivity with alternate connections and meshed links. However, in all cases, a certain level of security, scalability, and minor delay in the information and bi-directional data transfer capabilities is required. While information capability performs digital monitoring of SST variables (as in SCADA systems), the

Solid-State Transformer for Energy Efficiency Enhancement

DOI: http://dx.doi.org/10.5772/intechopen.84345

bi-directional data transfer capability allows fast responses to disturbances such that system's performance can be improved accordingly [27]. In fact, the smart grid (SG) concept is based on reliable real-time data availability and utilization for more

There could be two forms of communication in SST networks: wired or wireless. Their selection depends on the bandwidth and the cost of the telecommunications infrastructure [28]. In the wired case, there are technologies based on power line communications (PLC) and optical communications and digital subscriber line (DSL) [29]. Table 10 shows the comparison of wired communication technologies for smart grids according to coverage range and maximum theoretical data transmission. It is observed that optical fiber main application is the connectivity between transmission/distribution substations, thus, forming large coverage areas satisfying very high volumes of data and low latency. However, the main disadvantage is its high installation and equipment costs. On the other hand, PLC and DSL are technologies that can be merged on existing copper-wired networks, but their

In the case where the installation is above ground level, SSTs could have a wireless communication system. In fact, whenever possible, wireless technologies are preferred due to its flexibility and low cost; they can cover difficult access areas (distant or inaccessible) in power system monitoring applications [31]. As an example, a multipoint to point (MP2P) communication system for SST-based power system is shown in Figure 17. There are several wireless technologies that depend on the coverage and data rate, and these technologies allow the adoption of the multilayer architecture for smart grid as shown in Table 10. In the case of an SST-control center communication network, it is also possible to incorporate different intelligent electronic devices (IEDs), remote terminal units (RTU), substation automation solutions (SAS), universal gateways, smart meters, etc. There will be an increased complexity in the network operation due to the large amounts of data. Hence, these types of applications will require higher reliabilities and lower

bigger limitations are scalability and network flexibility [30].

intelligent decision-making.

latencies.

Figure 17.

135

Communication network for SST.
